1. Field of the Invention
The present invention relates to a liquid crystal display device and, more particularly, to a liquid crystal display device which is improved in yield factor by preventing disconnection from occurring in a layered line portion or a lead terminal portion in a liquid crystal display device of an active matrix type such as a thin-film transistor (TFT) type.
2. Description of the Related Art
Liquid crystal display devices are widely used as display devices for notebook personal computers, desktop personal computers and other electronic equipment because the liquid crystal display devices have advantages such as thin size, light weight, high contrast, fast response and the capability to reproduce moving images as well as high resolution which compares with cathode ray tubes.
Liquid crystal display devices are basically classified into two types: the type in which a liquid crystal layer is interposed between two substrates at least one of which is made of transparent glass or the like, and predetermined pixels are turned on or off by selectively applying voltage to various kinds of pixel-forming electrodes formed over the substrates (this type is called the simple matrix type); and the type in which such various kinds of electrodes and pixel-selecting switching elements are formed and predetermined pixels are turned on or off by selectively driving these switching elements (this type is called the active matrix type in which so-called thin-film transistors (TFTs) or so-called MIM diodes are used as the switching elements).
The latter active matrix type of liquid crystal display device has become a leading liquid crystal display device because of its contrast performance and its high-speed display performance.
In general, the active matrix type of liquid crystal display device is a vertical electric field type which includes at least a liquid crystal panel and a driving circuit. The liquid crystal panel is made of: an active matrix substrate over which gate lines, a gate insulating layer, a semiconductor layer, a contact layer, source and drain lines, a passivation layer and a pixel electrode layer are formed on one substrate in that order; a color filter substrate over which are formed color filter layers for plural kinds of colors, a black matrix for separating the color filter layers from one another, and a common electrode layer on the other insulative substrate; and a liquid crystal layer sealed in the gap between the active matrix substrate and the color filter substrate. The driving circuit serves to apply display signals for controlling the direction of molecular alignment of the liquid crystal layer to the various kinds of electrodes formed over the active matrix substrate and the color filter substrate. In the vertical electric field type, an electric field for changing the direction of alignment of liquid crystal molecules which constitute the liquid crystal layer is applied between the electrodes formed over the active matrix substrate and the electrodes formed over the other substrate.
In recent years, a lateral electric field type (In-Plane Switching Mode: IPS type) of liquid crystal display device has been put into practice, in which a direction in which to apply an electric field to its liquid crystal is made nearly parallel to the surface of a substrate. In this lateral electric field type of liquid crystal display device, a common electrode to be formed on the other substrate (color filter substrate) in the vertical electric field type of liquid crystal display device is formed on an active matrix substrate as a counter electrode, and a pixel electrode and the counter electrode are arrayed in a comb-tooth-like shape to control the direction of alignment of liquid crystal molecules in a plane parallel to the substrate.
In this type of liquid crystal display device, since the intersections of gate lines and drain lines are formed between adjacent pixels over the active matrix substrate, it is important that the breakdown voltage of the passivation layer (CVD insulating layer) between the gate lines and the drain lines be sufficiently high.
FIG. 14 is a plan view illustrating the essential portion of one example of the construction of an intersection of a gate line and a drain line in a pixel area of a related-art liquid crystal display device which uses thin-film transistors as switching elements, and FIG. 15 is a cross-sectional view taken along line A-Axe2x80x2 of FIG. 14.
As shown in FIG. 15 taken along line A-Axe2x80x2 of FIG. 14, in the intersection of a gate line and a drain line, a gate line 2, a gate insulating layer 3, a semiconductor layer 4, a contact layer 5, a drain layer 6, a source electrode 7 and a passivation layer 8 are formed over a lower transparent insulative substrate 1 which is an active matrix substrate.
In FIG. 14, reference numeral 9 denotes a contact hole for connecting a pixel electrode 10 and the source electrode 7, and reference numeral 11 denotes a light shield layer.
In addition, the surfaces of terminal lead lines, which are formed outside the pixel area of a liquid crystal panel in which a liquid crystal is sealed, are covered with an insulating material such as a resin so that the terminal lead lines are isolated from external impact or moisture contained in the air.
FIG. 16 is a diagrammatic cross-sectional view illustrating an example of the construction of an outside portion of the pixel area of the liquid crystal panel, and FIG. 17 is an enlarged cross-sectional view of the essential portion of FIG. 16. In FIGS. 16 and 17, reference numeral 1 denotes an active matrix substrate, reference numeral 14 an upper transparent insulative substrate which is a color filter substrate, reference numeral 15 denotes a liquid crystal layer, reference numeral 16 a sealing material, reference numeral 17 a driver chip, reference numeral 18 an epoxy resin, reference numeral 19 a conductor layer, and reference numeral 20 a bump.
As shown in FIGS. 16 and 17, the liquid crystal layer 15 is interposed between the active matrix substrate 1 and the color filter substrate 14, and is sealed along its periphery by the sealing material 16. The driver chip 17 is disposed in the periphery of the active matrix substrate 1, and is connected to a terminal line which is led from the pixel area inside the sealing material 16.
The liquid crystal panel is covered with the epoxy resin 18 on its sealing-material side and on the side on which the driver chip 17 is disposed, whereby the pixel area and the driver chip are isolated from external impact and moisture contained in the air.
As shown in FIG. 15, in case that a minute defect is present in the gate insulating layer 3 at the intersection of the gate line 2 and the drain line 6 in an individual pixel of the pixel area, the gate line 2 and the drain line 6 will be electrically shorted or a leak current will flow therebetween when a voltage is applied to both lines as indicated by an arrow C, because the breakdown voltage of the gate insulating layer 3 is low. This defect frequently occurs in an edge portion in which the drain line 6 passes over the gate line 2.
At this time, in case that a defect is present in the passivation layer 8 as indicated by an arrow A, there will occur the problem that moisture contained in the air penetrates through the portion of the detect of the passivation layer 8 and the drain line 6 breaks down by an electrolytic corrosion action as indicated by an arrow B.
Another problem is that, in the peripheral portion of the liquid crystal panel, as shown by the left-hand one of arrows A in FIG. 17, a crack is formed in the passivation layer 8 at the edge portion of the epoxy resin 18 by the stress thereof and moisture contained in the air penetrates through the crack and an electrolytic corrosion occurs in the drain line 6, thus leading to the disconnection of the drain line 6. A similar problem occurs on a lead-terminal side of the gate line 2.
As shown in FIG. 17, the bump 20 of the driver chip 17 is connected to a terminal line (the drain line 6) which is led to the periphery of the active matrix substrate 1, via a conductor layer 19 which extends through a through-hole formed in the passivation layer 8.
This driver chip mounting portion as well as the driver chip 17 is coated with the insulating layer 18 of an epoxy resin. This also results in the problem that, as shown-by the right-hand one of the arrows A in FIG. 17, a crack is formed in the passivation layer 8 at the edge portion of the epoxy resin 18 by the stress thereof and moisture contained in the air penetrates through the crack and an electrolytic corrosion occurs in the drain line 6, thus leading to the disconnection of the drain line 6.
The invention aims to provide a highly reliable liquid crystal display device by solving the problems of the related art and preventing electrolytic corrosions from occurring at the intersections of gate lines and drain lines or in a lead terminal portion over an active matrix substrate.
Therefore, the invention prevents moisture from penetrating toward an electrode or a lead terminal portion through a passivation layer by coating the passivation layer with ITO. In order to solve the above-mentioned problems, the present invention takes chiefly the following means.
(1) A liquid crystal display comprising a pair of substrates, a liquid crystal layer interposed between said pair of substrates, a gate line formed on one of said pair of substrate, a first insulating layer covering said gate line, a drain line formed on said first insulating layer, a second insulating layer covering said drain line, a pair of electrodes disposed between said pair of electrodes, wherein a portion of said drain line is intersected with said gate line, and an electrically conductive layer is formed on said second insulating layer and at least said portion.
(2) A liquid crystal display comprising, a pair of substrates, a liquid crystal layer interposed between said pair of substrates, a gate line formed on one of said pair of substrate, a first insulating layer formed over said gate line, a drain line formed on said first insulating layer, a second insulating layer formed over said drain line, a pair of electrodes disposed between said liquid crystal layer and one of said pair of substrates, wherein a black matrix formed on another of said pair of substrates and shielding said gate line and said drain line, and a portion of said drain line is intersected with said gate line, and an electrically conductive layer is formed on said second insulating layer and covering at least said portion.
(3) A liquid crystal display comprising, a pair of substrates, a liquid crystal layer interposed between said pair of substrates, a gate line formed on one of said pair of substrate, a common line formed on one of said pair of substrate, a first insulating layer formed on said common line, a drain line formed on said first insulating layer, a second insulating layer formed on said drain line, a pixel electrode formed on said first insulating layer, a counter electrode formed on one of said pair of substrate, wherein a portion of said drain line is intersected with said common line, and a black matrix formed on another of said pair of substrates and shielding said common line and said drain line, and an electrically conductive layer is formed on said second insulating layer and covered at least said portion.
1. (4) A liquid crystal display comprising, a pair of substrates, a liquid crystal layer interposed between said pair of substrates, a plurality of gate line formed on one of said substrates, extend to form a gate pad, a plurality of drain line formed on one of said substrates, extend to form a drain pad, an insulating layer covering said gate line and said drain line, a plurality of pixel electrodes formed on said insulating layer, wherein an electrically conductive layer formed on said gate line adjacent to said gate pad, and a resin covering at least a portion of an edge of said electrically conductive layer.
(5) A liquid crystal display comprising, a pair of substrates, a liquid crystal layer interposed between said pair of substrates, a plurality of gate line formed on one of said substrates and extended to form a gate pad, a plurality of drain line formed on one of said substrates and extend to form a drain pad, a pair of electrodes formed on one of said substrates, an insulating layer covering said gate line, said drain line and at least one of said pair of electrodes, wherein an electrically conductive layer formed on said drain line adjacent to said drain pad, and a resin covering at least a portion of an edge of said electrically conductive layer.
Moreover, the liquid crystal display device according to the invention has any of constructions which will be described below in Paragraphs (6) to (10).
(6) A liquid crystal display device includes at least a liquid crystal panel and a driving circuit. The liquid crystal panel is made of: one insulative substrate over which an interconnection of a gate line and a drain line is formed to have a structure in which the gate line, a gate insulating layer, a semiconductor layer, a contact layer, the drain line and a passivation layer are stacked in that order from the insulative-substrate side; another insulative substrate over which are formed color filter layers for plural kinds of colors, a black matrix for separating the color filter layers from one another, and a common electrode layer; and a liquid crystal layer sealed in the gap between both substrates, The driving circuit serves to apply display signals for controlling the direction of molecular alignment of the liquid crystal layer to the various kinds of electrodes formed in the liquid crystal panel. The liquid crystal display device further includes a capping layer which is made of the same ITO layer as the pixel electrode layer and is formed over the passivation layer at the intersection of the gate line and the drain line which are formed over the one substrate.
According to this construction, in the process of manufacturing the one substrate over which the gate line and the drain line are formed, moisture contained in the air is prevented from penetrating toward the gate line and the drain line through the passivation layer, and electrolytic corrosion of the drain line in particular is prevented, whereby it is possible to provide a highly reliable liquid crystal display device.
(7) A liquid crystal display device includes at least a liquid crystal panel and a driving circuit. The liquid crystal panel is made of: one insulative substrate over which an interconnection of a gate line and a drain line is formed to have a structure in which the gate line, a gate insulating layer, a semiconductor layer, a contact layer, the drain line and a passivation layer are stacked in that order from the insulative-substrate side; another insulative substrate over which are formed color filter layers for plural kinds of colors, a black matrix for separating the color filter layers from one another, and a common electrode layer; and a liquid crystal layer sealed in the gap between both substrates. The driving circuit serves to apply display signals for controlling the direction of molecular alignment of the liquid crystal layer to the various kinds of electrodes formed in the liquid crystal panel. The liquid crystal display device further includes a capping layer which is made of an ITO layer and is formed over the passivation layer formed over a lead terminal line at the periphery of a pixel area of the one substrate.
According to this construction, neither electrolytic corrosion nor cracks occur in the lead terminal line which is led to the periphery of the pixel area after the manufacture of the liquid crystal panel, whereby it is possible to provide a highly reliable liquid crystal display device.
(8) A liquid crystal display device includes at least a liquid crystal panel and a driving circuit. The liquid crystal panel is made of: one insulative substrate over which an interconnection of a gate line and a drain line is formed to have a structure in which the gate line, a gate insulating layer, a semiconductor layer, a contact layer, the drain line and a passivation layer are stacked in that order from the insulative-substrate side; another insulative substrate over which are formed color filter layers for plural kinds of colors, a black matrix for separating the color filter layers from one another, and a common electrode layer; and a liquid crystal layer sealed in the gap between both substrates. The driving circuit serves to apply display signals for controlling the direction of molecular alignment of the liquid crystal layer to the various kinds of electrodes formed in the liquid crystal panel. The liquid crystal display device further includes a capping layer which is made of the same ITO layer as the pixel electrode layer and is formed over the source electrode and under the passivation layer at the intersection of the gate line and the drain line which are formed over the one substrate.
According to this construction, in the process of manufacturing the one substrate over which the gate line and the drain line are formed, moisture contained in the air is prevented from penetrating toward the gate line and the drain line, and electrolytic corrosion of the drain line in particular is prevented, whereby it is possible to provide a highly reliable liquid crystal display device.
(9) A liquid crystal display device includes at least a liquid crystal panel and a driving circuit. The liquid crystal panel is made of: one insulative substrate over which an interconnection of a gate line and a drain line is formed to have a structure in which the gate line, a gate insulating layer, a semiconductor layer, a contact layer, the drain line and a passivation layer are stacked in that order from the insulative-substrate side, another insulative substrate over which are formed color filter layers for plural kinds of colors, a black matrix for separating the color filter layers from one another, and a common electrode layer; and a liquid crystal layer sealed in the gap between both substrates. The driving circuit serves to apply display signals for controlling the direction of molecular alignment of the liquid crystal layer to the various kinds of electrodes formed in the liquid crystal panel. The liquid crystal display device further includes a capping layer which is made of an ITO layer and is formed between lead terminal lines and under the passivation layer formed over the lead terminal lines at the periphery of a pixel area of the liquid crystal panel.
According to this construction, neither electrolytic corrosion nor cracks occur in the lead terminal lines which are led to the periphery of the pixel area after the manufacture of the liquid crystal panel, whereby it is possible to provide a highly reliable liquid crystal display device.
(10) In each of the constructions (6) (7) (8) and (9), the capping layer is formed to have a width equal to or greater than the line width of the underlying conductor layer.
According to this construction, moisture contained in the air is prevented from penetrating toward the gate line and the drain line during the process of manufacturing the one substrate, as well as moisture contained in the air is prevented from penetrating toward a lead terminal portion after the sealing of the liquid crystal panel with a sealing material, whereby it is possible to prevent the occurrence of disconnection due to electrolytic corrosion as well as the occurrence of disconnection in a lead terminal due to stresses caused by the curing of the resin applied to the periphery of the liquid crystal panel and a driver chip mounting portion. Accordingly, it is possible to provide a highly reliable liquid crystal display device.
According to each of the constructions of the invention, it is possible to efficiently prevent disconnection or the like due to electrolytic corrosion or stress caused by the penetration of moisture toward the gate line, the drain line, the intersection of both lines in the pixel area or the conductor layer of a lead terminal.
If foreign matter is present near the gate line, the drain line and the intersection of both lines and a current leak occurs in the gate insulating layer, there are cases in which the passivation layer abnormally grows owing to the foreign matter and a pinhole is formed in the abnormal portion of the passivation layer. There is a strong possibility that pinholes are formed in a gate line portion where the coverage of a CVD layer is inferior. Moreover, at the intersection of the gate line and the drain line, there is a possibility that the drain line is formed above a pinhole and a pinhole is also formed in the overlying passivation layer.
If a pinhole is formed, moisture contained in the air easily penetrates into a portion below the passivation layer through the pinhole, and static electricity occurs in this portion during the manufacture of an active matrix substrate or an electrochemical corrosion reaction (electrolytic corrosion) occurs when electricity flows through the lines during a continuity test after the manufacture, so that the lines are broken down. To prevent this breakdown, it is only necessary to block the supply of moisture which is a main cause of electrolytic corrosion.
In the invention, at the same time that pixel electrodes are formed, a capping layer (protective layer: also called a cap layer) made of a transparent conductive layer is formed over the portion of a passivation layer in which electrolytic corrosion easily occurs. If a pinhole is formed in a portion of the passivation layer, the pinhole is buried by a pattern of the transparent conductive layer formed in that portion, whereby the supply of moisture is intercepted. To completely cap (cover) a portion where a pinhole occurs, it is only necessary to make the width of the capping layer larger than that of the drain line.
In addition, by disposing the capping layer in the pinhole portion, it is possible to prevent diffusion of impurities into an alignment layer and the liquid crystal layer from the active matrix substrate underlying the passivation layer. If alkali metal ions which are contaminant elements or metal ions from metal layers which form the lines penetrate the liquid crystal layer through a pinhole, the electric conductivity of the liquid crystal layer decreases to cause a defective display. Since the source of the metal ions is very uneven, contaminant elements are easily stored in the source, and further, there is a strong possibility that the electrolytic corrosion occurs at the intersection of a gate line and a drain line which are easily supplied with metal ions by the electrolytic corrosion. Accordingly, it is possible to restrain the occurrence of a defective display by capping such an intersection portion with an electrically stable oxide transparent conductive layer (such as indium tin oxide: ITO).
If the capping layer is to be formed from the same layer as the pixel electrodes, it is preferable to form the capping layer at the intersections of gate lines and drain lines in portions where pixel electrodes are absent, because if the capping layer contacts a pixel electrode, the pixel capacitance thereof varies to cause a spot defect.
It is to be noted that the capping layer which is formed in the pixel area need not necessarily be the same layer as the pixel electrode, and can also be formed independently of the ITO layer from which the pixel electrode is formed.
In a case where a lateral electric field is to be applied as means for controlling the molecular alignment of a liquid crystal, each pixel electrode is formed of a common electrode and a source electrode each having a comb-teeth-like shape. In this case, since no pixel electrode is formed over the passivation layer, a capping layer can be widely formed over the passivation layer without forming a short-circuit between adjacent pixels. Accordingly, in the case of the lateral electric field type, a capping layer made of a transparent conductive layer can be widely formed over each of drain and gate lines. Since this capping layer can be formed at the same time as a terminal conductive coating layer, the number of manufacturing steps need not be increased.